Isotopic exchange in mineral-fluid systems: III. Rates and mechanisms of oxygen isotope exchange in the system granite-H sup 2 O + KCl at hydrothermal conditions

Journal Article · Wed Jan 01 00:00:00 EST 1992 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(92)90144-8· OSTI ID:5077825

Cole, D R; Jacobs, G K ^[1]; Ohmoto, Hiroshi ^[2]

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1. Oak Ridge National Lab., TN (United States)
2. Pennsylvania State Univ., University Park (United States) Tohuku Univ., Sendai (Japan)

Variations with time in the alteration mineralogy and the oxygen isotopic composition of solutions, minerals, and rocks have been experimentally investigated at T = 170 to 300C, P = L/V to 0.3 kb, water/rock mass ratios (0.2 to 6), and grain sizes ({approximately} 0.1 mm to 2.5 mm) for periods up to 1,006 h. Alteration assemblages formed in the experiments are dominated by chlorite (after biotite), sericite-zeolite-albite (after K-feldspar and plagioclase), and hematite (after magnetite and pyrite). Reaction of rock and aqueous solution resulted in depletion of {sup 18}O in the solid and enrichment of {sup 18}O in the fluid. The magnitudes of change increase as temperature, time, salt concentration, and surface area increase. The trends in isotopic shifts are directly related to changes in the style and intensity of mineralogic alteration in the granite. The degree of isotope exchange in the experimental systems between granite (minerals) and solutions was computed from the comparison with calculated equilibrium fractionation factors and yield values of less than 5 to 50% exchange. The {delta}{sup 18}O changes of the rocks, minerals, and fluid were observed to follow closely with those expected from a first-order rate law. Based on a simple closed-system model with (W/S) mass ratios between 0.5 and 5, the authors estimate the minimum time required for granite-fluid isotopic equilibration to be roughly 200 years or less for grains 1 cm in radius or smaller (porous-media analog) reacted at 300C, and between 10{sup 4} and 10{sup 5} years for grains ranging from 0.1 to 1 m in radius (fractured-media analog) reacted at 300C.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 5077825
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 56:1; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
58 GEOSCIENCES
BRINES
ROCK-FLUID INTERACTIONS
GRANITES
OXYGEN 18
ISOTOPIC EXCHANGE
ALBITE
ANORTHOSITES
AQUEOUS SOLUTIONS
BENCH-SCALE EXPERIMENTS
BIOTITE
CHEMICAL REACTION KINETICS
CHLORITE MINERALS
ENRICHMENT
EQUILIBRIUM
EXPERIMENTAL DATA
FELDSPARS
HEMATITE
HYDROTHERMAL ALTERATION
MINERALOGY
POTASSIUM CHLORIDES
QUANTITY RATIO
SODIUM CHLORIDES
SURFACE AREA
TEMPERATURE DEPENDENCE
TIME DEPENDENCE
WATER
ZEOLITES
ALKALI METAL COMPOUNDS
CHLORIDES
CHLORINE COMPOUNDS
DATA
DISPERSIONS
EVEN-EVEN NUCLEI
GABBROS
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
INFORMATION
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
IRON ORES
ISOTOPES
KINETICS
LIGHT NUCLEI
MATERIALS
MICA
MINERALS
MIXTURES
NUCLEI
NUMERICAL DATA
ORES
OXIDE MINERALS
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PLUTONIC ROCKS
POTASSIUM COMPOUNDS
REACTION KINETICS
ROCKS
SILICATE MINERALS
SODIUM COMPOUNDS
SOLUTIONS
STABLE ISOTOPES
SURFACE PROPERTIES
152001* - Geothermal Data & Theory- Properties of Aqueous Solutions
580000 - Geosciences